[argyllcms] Re: Lost shadow detail in PS CS2 with Lab profile

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 30 Dec 2009 12:55:47 +1100

Vallo Kallaste wrote:

Now this is getting hairy. I've converted bunch of raw's and saved them as
16bpc TIFF's with embedded "Chrome 2000 D50.icm" profile. Are you saying
that I should create one monitor profile for every source profile I
possibly could come accross? In current case use "Chrome 2000 D50.icm"
profile as the source one, as argument for the -S switch? I don't actually
understand what the following constraint in colprof manual means:

Yep, if you want actual gamut mapping using ICC device profiles,
that's what you have to do. It's the basic nature of them that they
have static gamut mappings cooked into their B2A tables.
[Not very convenient eh ? That's why WCS went for dynamic linking,
 although ICC V4 with the PRMG can partially solve the problem too.]

Note that a input, output, display or device colororspace profile should
be specified, not a non-device colorspace, device link, abstract or named
color profile.

What kind of profile the "Chrome 2000 D50.icm" actually is? In the raw
converter sense it's output profile.

Without examining the profile it's hard to say. (ie. use iccdump on it).

What about that bwtest.jpg image which has embedded "Gray Gamma 2.2"
profile? Should I extract the embedded profile (or convert the file to
TIFF leaving the profile intact) and use that profile (or TIFF) as
argument for -S switch while creating cLUT profile?

I suspect that using a monochrome profile will not succeed, because I probably
haven't made provision for that special case. [It wouldn't be reasonable
to force such a display profile to convert everything to monochrome, but
a monochrome source profile doesn't define a 3D gamut, so some fudge would
be needed to partially gamut map.]

I think that I understand the need for PCS space, A2B/B2A tables and
different mapping intents, but seems I'm not able to map that
understanding back to real life. I'm not rocket scientist, only lone
UNIX systems admin trying to get hang of it :)

There are a few basic concepts to get a grasp of. What a gamut is, and
how the different intents typically work, and the limitations of the
different ICC profile formats (matrix vs. cLUT) seems to be the next step.

Graeme Gill.

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